Bt for spongy moth (gypsy moth)
Btk works well only on young caterpillars, and on large trees it needs a licensed applicator with the right equipment. UMass Extension's test is the head: all-black heads mean the spray will work, and yellow markings mean it is late. About 90% of the feeding happens in the last two instars, so a spray in late June mostly misses. Cover the foliage thoroughly, and let the fungus Entomophaga maimaiga do the rest in a wet spring.
Before you order
A bacterium sprayed on leaves. Caterpillars that eat it stop feeding and die within a few days. It works only on the larvae of moths and butterflies, and has little or no effect on bees, lady beetles, lacewings or parasitic wasps. How it works, how to tell it has established and the supplier list are on the full Bacillus thuringiensis kurstaki profile.
Other controls for spongy moth
No other reviewed control is listed for this pest yet.